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Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator
Daily cone-beam computed tomography (CBCT) is mandatory for cancer patients receiving radiotherapy treatment using advanced techniques on the Varian Halcyon linear accelerator for setup verification, correction, and adaptation of the treatment plan. The frequent nature of imaging sessions mostly usi...
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| Format: | Thesis |
| Language: | English English |
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Division of Radiology
2025
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| _version_ | 1867613165730136064 |
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| access_status_str | Open Access |
| author | Mbewe, Jonathan |
| author2 | Groenewald, Anne-Mari |
| author_browse | Groenewald, Anne-Mari Mbewe, Jonathan |
| author_facet | Groenewald, Anne-Mari Mbewe, Jonathan |
| author_sort | Mbewe, Jonathan |
| collection | Thesis |
| description | Daily cone-beam computed tomography (CBCT) is mandatory for cancer patients receiving radiotherapy treatment using advanced techniques on the Varian Halcyon linear accelerator for setup verification, correction, and adaptation of the treatment plan. The frequent nature of imaging sessions mostly using kilovoltage (kV) x-ray energies has raised concerns about the contribution of low-energy radiation dose to the overall integral dose and possible induction of secondary primary tumours. In this study, the dose to organs and tissues located in the pelvic and thoracic regions of the body from kV CBCT imaging was estimated using the GATE Monte Carlo toolkit. The spectral, dose output, and filtration characteristics of the x-ray source on the Halcyon kV CBCT system were derived through measurements using a calibrated ionisation chamber and analytical calculations. The outcomes of this process were used to build a geometry for the Monte Carlo model of the beamline, and then validate it by comparing the computed Percentage Depth Dose and Crossline profiles to those measured in a water phantom using calibrated parallel plate and thimble ionisation chambers. In-phantom dose measurements using Radiochromic film in RANDO pelvic and thoracic phantoms were used to generate a Normalisation Factor to relate the measured and simulated absorbed doses. To estimate the patient doses, Monte Carlo simulations were performed on the Adult Female reference computational phantom from the International Commission for Radiation Protection (ICRP) publication 110. The highest doses to the pelvic region resulted from the “Pelvis Large” imaging protocol, with organ doses ranging from 5.11 mGy to 174.96 mGy per CBCT scan. In the thoracic region, the “Thorax” protocol resulted in the highest doses, ranging from 2.75 mGy to 54.63 mGy per CBCT scan. Depending on the fractionation regimen in use, there is a possibility that the imaging doses may exceed 5% of the prescribed therapeutic dose, in which case the imaging dose may need to be added to the treatment plan per recommendation of the AAPM Task Group 180 report. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/42415 |
| institution | University of Cape Town (South Africa) |
| language | English eng |
| last_indexed | 2026-06-10T12:31:48.735Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Division of Radiology |
| publisherStr | Division of Radiology |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/42415 Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator Mbewe, Jonathan Groenewald, Anne-Mari Radiation Medicine Daily cone-beam computed tomography (CBCT) is mandatory for cancer patients receiving radiotherapy treatment using advanced techniques on the Varian Halcyon linear accelerator for setup verification, correction, and adaptation of the treatment plan. The frequent nature of imaging sessions mostly using kilovoltage (kV) x-ray energies has raised concerns about the contribution of low-energy radiation dose to the overall integral dose and possible induction of secondary primary tumours. In this study, the dose to organs and tissues located in the pelvic and thoracic regions of the body from kV CBCT imaging was estimated using the GATE Monte Carlo toolkit. The spectral, dose output, and filtration characteristics of the x-ray source on the Halcyon kV CBCT system were derived through measurements using a calibrated ionisation chamber and analytical calculations. The outcomes of this process were used to build a geometry for the Monte Carlo model of the beamline, and then validate it by comparing the computed Percentage Depth Dose and Crossline profiles to those measured in a water phantom using calibrated parallel plate and thimble ionisation chambers. In-phantom dose measurements using Radiochromic film in RANDO pelvic and thoracic phantoms were used to generate a Normalisation Factor to relate the measured and simulated absorbed doses. To estimate the patient doses, Monte Carlo simulations were performed on the Adult Female reference computational phantom from the International Commission for Radiation Protection (ICRP) publication 110. The highest doses to the pelvic region resulted from the “Pelvis Large” imaging protocol, with organ doses ranging from 5.11 mGy to 174.96 mGy per CBCT scan. In the thoracic region, the “Thorax” protocol resulted in the highest doses, ranging from 2.75 mGy to 54.63 mGy per CBCT scan. Depending on the fractionation regimen in use, there is a possibility that the imaging doses may exceed 5% of the prescribed therapeutic dose, in which case the imaging dose may need to be added to the treatment plan per recommendation of the AAPM Task Group 180 report. 2025-12-08T09:09:18Z 2025-12-08T09:09:18Z 2025 2025-12-08T09:00:51Z Thesis / Dissertation Masters MSc http://hdl.handle.net/11427/42415 en eng application/pdf Division of Radiology Faculty of Health Sciences University of Cape Town |
| spellingShingle | Radiation Medicine Mbewe, Jonathan Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator |
| thesis_degree_str | Master's |
| title | Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator |
| title_full | Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator |
| title_fullStr | Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator |
| title_full_unstemmed | Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator |
| title_short | Assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the Varian Halcyon linear accelerator |
| title_sort | assessment of imaging dose from the kilovoltage cone beam computed tomography system on board the varian halcyon linear accelerator |
| topic | Radiation Medicine |
| url | http://hdl.handle.net/11427/42415 |
| work_keys_str_mv | AT mbewejonathan assessmentofimagingdosefromthekilovoltageconebeamcomputedtomographysystemonboardthevarianhalcyonlinearaccelerator |